Method for adding alloying elements to molten metals

ABSTRACT

A METHOD FOR ADDING ALLOYING ELEMENTS SUCH AS ALUMINIUM, TITANIUM TO MOLTEN METALS, SAID ELEMENTS BEING CAPABLE OF REACTING WITH THE ATMOSPHERE SURROUNDING THE METALS, COMPRISING INSERTING A WIRE ROD MADE OF THE ELEMENT INTO A MOLTEN METAL BATH AT A CONTROLLED SPEED,   SAID ROD HAVING A CONTROLLED IZE, SO AS TO PRODUCE A REFINED AND PURIFIED METAL ALLOY.

April 24, 1973 TAKAHO KAWAWA 3,729,309

METHOD FOR ADDING ALLOYING ELEMENTS TO MOLTEN METALS Filed March 2, 1970 5 Sheets-Sheet 1 /Gji INVENTOR 77% KA H0 KAwAwA ATTORNEYS April 24, 1973 TAKAHO KAWAWA METHOD FOR ADDING ALLOYING ELEMENTS TO MOLTEN METALS 5 Sheets-Sheet 2 Filed March 2, 1970 INVENTOR TA AHfi AK/4W4 BY +1 ATTORNEYS April 24, 1973 TAKAHO KAWAWA METHOD FOR ADDING ALLOYING ELEMENTS TO MOLTEN METALS 5 Sheets-Sheet Filed March 2, 1970 b \JUQQSwoCK INVENTOR 3mm 0 KAWAWA BY ATTORNEY 5 April 24, 1873 TAKAHO KAWAWA 3,729,309

METHOD FOR ADDING ALLOYING ELEMENTS TO MOLTEN METALS Filed March 2. 1970 Sheets-Sheet 4 L 40- L 1 2 l t l l l 1O $0 20 & k m

INVENTOR 7; KA #0 KAWAVJA ATTORNEYS April 1973 TAKAHO KAWAWA 3,729,309

METHOD FOR ADDING ALLOYING ELEMENTS To MOLTEN METALS Filed March 1970 5 Sheets-Sheet 5 T, Q Q, 20! D 0 Q; L W0- INVENTOR 2K A H- a KAwn W4 ATTORNEYJ United States Patent US. Cl. 75-129 7 Claims ABSTRACT OF THE DISCLOSURE A method for adding alloying elements such as aluminium, titanium to molten metals, said elements being capable of reacting with the atmosphere surrounding the metals, comprising inserting a wire rod made of the element into a molten metal bath at a controlled speed, said rod having a controlled size, so as to produce a refined and purified metal alloy.

This invention relates to a method for adding alloying elements to molten metals during a refining procedure. More particularly, it relates to the addition of such elements which are liable to be converted into either a nitride or oxide by reaction with the atmosphere ambient to the molten metals in a container such as a ladle.

The said alloying elements, i.e., Si, Al, Ti, V, La, Nb, or alloys containing one or more of the above have been added in the form of a lump, a bar or the like to molten steel by conventional methods, wherein they are either added directly to the molten metals tapped into a ladle or placed in a ladle prior to the teeming. By these conventional methods, the yield of Al and Ti is low and unstable because of the ready reaction thereof with the atmosphere, although various shapes of Al and Ti have been proposed in order to promote a high yield in steelmaking.

The low and unstable yield of Al and Ti results from an oxidation loss caused by their reaction with either oxygen or oxidizing slag in the molten steel or the atmosphere surrounding the molten steel during tapping. The dimensions of the atmosphere involved during tapping is 20 to 30 times larger than that of the molten steel, thus leading to a large oxidation loss. In the case of Ti and Ti alloy, the oxidation loss is increased by a reaction with nitrogen in the atmosphere.

For the above discussed reasons, it is expensive to produce a steel alloy containing elements with a high oxidizing or nitriding capacity, such as Ti and Al, by conventional methods. Moreover, Al, Ti and their alloys react with the atmosphere to form a great amount of A1 0 TiO and TiN. The amount of the respective alloying elements is unstable in the molten steel, which decreases the quality of the steel alloys.

This invention relates to a method of adding alloying elements, liable to react with the atmosphere, to the initially refined molten metals. In the method of the invention Al, Ti and alloys containing the same are added to the molten steel in the form of a wire rod at a speed ranging from 2.5 to 50 m./sec. While the steel is stirred.

FIGS. 2 to 4 are cross-sectional views of different stirring devices;

FIG. 5 is a graph showing the deviation of Sol. Al in a steel alloy using a conventional method;

FIG. 6 is a graph showing deviation of S01. Al in a steel alloy using a method embodying this invention;

FIG. 7 is a graph showing deviation of Ti in a steel alloy obtained by a conventional method; and

FIG. 8 is a graph showing deviation of Ti in a steel alloy obtained by a method embodying the present invention.

Referring now to FIG. 1, the primary refining procedure is completed in a furnace 1, wherein the necessary alloying elements are added prior to theaddition of the elements, liable to be transformed into nitride or oxide, in such a way as to improve the yield of the latter elements. Said primarily refined molten metals are transferred from the furnace to a ladle 2, having a porous refractory material 3 forming part of its surface. Through the refractory materials gases which are harmless to the steels, such as Ar and N are blown. The alloying agents in the shape of wire are fed through a reel 4 and guides 4, 5 and 7 by means of a wire feed device 6 and inserted into the molten steel or iron at high speed.

It should be noted that the diameter of said wire rod ranges from 3 to 20 mm. and the adding speed ranges from 2.5 to 50 m./sec. A wire rod of less than 3 mm. in diameter is apt to be entangled in the guide 7 and cannot be fed with ease, whereas one of more than 20 mm. in diameter cannot be bent along the guide 7 with ease. Alloying agents with a lower specific gravity than iron, especially Al and Ti, will float on to the molten steel surface and will not disperse throughout the steel if added at a speed of less than 2.5 m./ sec. If added at a speed of more than 50 m./sec., said alloying agents are concentrated at the point where the wire rod is inserted, and the extra alloy material floats on to the molten metal surface, thus impeding uniform distribution of the additive elements. Accordingly, the adding speed has to be controlled so as to promote uniform distribution of the alloy compositions.

In order to stir the molten steel in the ladle, various kinds of gas blowing devices are employed, e.g. a stopper type and a rotatable stopper type. The first type of ladle is provided with a porous refractory material 8 inside thereof as shown in FIG. 2 and the latter type of ladle is provided with the porous refractory material 8 at the end of the rotatable stopper as shown in FIG. 3. FIG. 4 shows an electric stirring system by means of a coil 10 supplying induction power to steel positioned in the ladle. In short, any stirring method for uniformly stirring the Whole molten steel in the ladle is applicable for the uniform dispersion of said alloying agents and oxidizing agents added at a high speed in the molten bath. A stirring system of this kind not only helps in the uniform dispersion of the alloy agents in the bath but also makes such inclusions as A1 0 Ti0 and TiN formed by A1 and Ti and their alloy additions float up to the surface, thus providing advantages in manufacturing refined and purified steel alloy.

In the method of the present invention, the alloying agents in the form of wire rod are directly dispersed throughout the molten steel without a reaction with slag or the atmosphere, thus improving the yield in steel making.

The invention is illustrated by the following examples.

3 EXAMPLE 1 Fe-Mn, Fe-Si and Al have been conventionally added in the form of bars of 1 kg. weight at the tapping stage of manufacturing steel plates for shipbuilding in a topblown converter of 100 ton weight. The deviation of said Sol. Al product by this method is shown in FIG. 5. On the contrary, the present invention provides a method in which only Fe-Mn and Fe-Si are added at the time of tapping and then Al wire rod of 10 mm. in diameter is added at a speed of -10 m./sec. over a period of five minutes after tapping while stirring the molten steel by argon or nitrogen gas blown by the device shown in FIG. 1. FIG. 6 shows the distribution of S01. Al in a product so produced. A comparison of FIGS. 5 and 6 shows the yield point of S01. Al is two times as high and the deviation is less by /2. It should be noted that the desired or aimed value of Al content is easily obtained. The oxygen content of conventional steel alloy is T(O)=50- -30 p.p.m. while that of the steel alloy produced by the method of the invention is (T(O)=30i-l5 p.p.m. Thus a good purified steel alloy is produced.

EXAMPLE 2 When AISI 321 steel produced in a 40 ton electric furnace is tapped into a ladle, bar-shaped Al and Fe-Ti alloy have been added simultaneously in the known method. By the present invention, the other alloying elements except Al and Ti are first added to a ladle in the conven tional way and then Al wire rod of 8 mm. in diameter is inserted at a speed of 5 m./sec. and Ti wire rod of mm. in diameter is inserted at the speed of 6 m./ sec. successively. This steel requires 5 times as much Ti addition as compared with carbon steel. FIG. 7 sho deviation of Ti in the steel by the conventional method and FIG. 8 shows the result obtained by the present invention. These two figures clearly indicate that the yield point is 4 times higher, the standard deviation of alloying elements is /5 times less. The desired value of each alloying element can easily be obtained by the present invention as compared with the prior art.

It should be noted that the method of this invention decreases formation of TiN in the molten metals because of the high speed addition of Ti wire rod to a ladle and produces 0.4 mm. cold rolled steel plates of greatly improved yield ranging from 90 to 95% as a result. A large amount of TiN inclusion occurs in known method because of reaction with the atmosphere and therefore only 60 to 80% of the 0.4 mm. cold rolled steel plates were rated as first class. These data show the advantages of the present method for the manufacture of 0.4 mm. cold rolled steel plates.

EXAMPLE 3 COMPARATIVE ANALYSIS OF MOLTEN METALS IN MOLDS [The mean value of 10 steel ingots] Sol. Al.

Al. percent content (standard Yield Oxygen (mean deviaof .Al, content, value) tion) percent percent Conventional method. 0. 044 0. 010 42 0. 0035 Present invention method. 0. 045 0. 00-t 63 0. 0025 N o'rE.-Yield of Al percent =(Sol. Al percent/added A1 percent) X100.

EXAMPLE 4 Titanium killed steel, namely AISI steel 321, is produced from a 14 ton steel ingot with less than 0.08%

COMPARATIVE ANALYSIS OF MOLTEN METALS IN MOLDS content Standard percent deviation Yield Oxygen (mean of Ti, of Ti, content, value) percent percent percent Conventional method 0. 41 0. 07 23. 1 0. 006 Present invention method- 0. 39 0. 01 91. 2 0. 003

EXAMPLE 5 The following table shows the comparative results in producing rimmed steels containing 0.05 to 0.06% of carbon, 0.30 to 0.50% of manganese and less than 0.020% of phosphorus and sulphur respectively.

ANALYSIS OF OXYGEN CONTENT (PERCENT) IN MOLD AND FIRST CLASS YIELD OF GOLD ROLLED STEEL Oxygen content First class (percent) :l: yield of standard cold rolled deviation steel plate, (percent) percent Conventional method 0. 053:1:0, 006 85. 5 Present invention method 0. 05210003 89. 4

Accurate control of S01. Al content means free control of the oxygen content of rimmed steel or semi-killed steel. Rapid analysis of the oxygen content of the molten metals prior to tapping facilitates manufacture of cold rolled steel plates of high quality both on the surface and internally with a much improved yield under the optimum rimming treatment based on the controlled oxygen content.

The method of the invention is applicable not only to A1 and Ti but also to any other metallic alloying element, which is liable to react upon the atmospheric conditions, and which is capable of being formed into a wire rod.

I claim:

1. A method of uniformly alloying molten steel in a molten bath thereof with an alloying element, said element being capable of reaction with the atmosphere above said bath, which comprises continuously feeding a wire rod of said alloying element and having a diameter ranging from 3 to 20 mm. into said molten steel bath at a speed of 2.5 to 50 meters per second, while separately stirring the whole of said molten steel bath by a means non'reactive with said molten steel bath so that as said wire rod is consumed upon entering said molten steel bath said bath is being stirred, thereby uniformly distributing said alloying element therein, thus permitting formation of a steel alloy of uniform predetermined composition.

2. A method as claimed in claim 1, wherein the alloying element is titanium.

3. A method as claimed in claim 1, wherein the alloying element is aluminium.

4. A method as claimed in claim 1, wherein the alloying element is selected from the group consisting of silicon, vanadium, lanthanum and niobium.

5. A method as claimed in claim 1, wherein a plurality of wires are fed successively into the molten steel bath.

6. Method according to claim 1 wherein said molten steel bath is stirred by blowing inert gas therethrough.

7. Method according to claim 1 wherein said molten steel bath is stirred by subjecting said molten steel bath to electrical induction.

(References on following page) References Cited UNITED STATES PATENTS Norbeck 7558 Reece 75--122 Feichtinger 75-46 Spire 7559 X Wever 73-23 X Hornak 7549 Feichtinger 7551 X 6 Hornak 7549 X Hoif 75129 X FOREIGN PATENTS France 164-57 US. Cl. X.R. 

